The present invention relates generally to the operation of gas lasers such as copper vapor lasers and more particularly to a system for controlling the flow of gas into and out of such lasers.
The gas laser such as a copper vapor laser requires a continuous in flow and out flow of gas, as exemplified diagrammatically in FIG. 1 which illustrates a typical copper vapor laser system. This system which is generally indicated by the reference numeral 1 is shown including an arrangement of components for causing neon gas to flow into and be leaked out the laser, which is generally indicated by the reference numeral 2, in a controlled manner so as to maintain the pressure within the laser at a particular level, for example 40 torr. The specific components utilized to control the gas flow into the laser include a supply of neon gas generally indicated at 3, a suitable and readily providably transducer 4 for sensing the pressure within the laser, an inlet valve 5 and readily providably control circuitry which is generally indicated at 6. The transducer, upon sensing the pressure within the laser, provides a corresponding signal which is utilized by circuitry 6 to control valve 5 in the appropriate manner. If the pressure within the laser is below the desired level, the valve is caused to increase the gas flow therein and if the pressure within the laser rises, the valve is caused to decrease the flow.
Thus far, only those components of system 1 which serves to control the flow of neon gas into laser 2 have been described. The components utilized to control the flow of gas out of the laser include a vacuum pump 7 and a control valve 8. The vacuum pump serves to draw the gas out of the laser through the control valve and the latter functions as a constriction device between the laser and pump. This constriction device serves to provide a relatively large drop in pressure between the laser and vacuum pump, for example a drop in pressure from 40 Torr to 1 Torr, while maintaining a constant gas flow rate over that drop in pressure, for example a flow rate of 10 sccm. In that way, a relatively low pressure vacuum pump can be utilized, for example one which operates at 1 torr or less.
The typical system just described has the advantage that it can utilize a relatively low pressure pump. However, the use of such a pump results in a particular problem associated with reverse molecular flow. Specifically, when vacuum pump 7 operates at low pressure, for example on the order of 1 torr or less, it operates within the molecular flow regime or region. As a result, molecules are able to flow upstream as well as downstream. Thus, it is possible for oil molecules from the vacuum pump to diffuse back into the laser system. In order to prevent this from occurring, a typical system of the type illustrated in FIG. 1 has been provided with a liquid nitrogen (L/N) trap between the vacuum pump and laser, as generally indicated by the reference numeral 9 in FIG. 1. This trap utilizes liquid nitrogen to condense the reverse flow oil within a cooperating trap, thereby preventing it from going any farther back into the system. While such a trap functions in the intended manner, it has a disadvantage of specialized maintenance and handling required plus high vacuum required to keep liquid nitrogen losses low and relatively large.